" Every photo you take with your digital camera contains hidden
information about the images (such as the settings used to take it)
and the camera (such as the make, model and unique serial number
used to identify it).
This is known as "exif" data. "

Now that I see this, I remember reading that someone whose camera was stolen found it by looking for its exif metadata in pictures on the internet. The exif metadata can be removed or altered, but whoever posted the pictures probably didn't know about exif metadata.

GQView is a small image viewing program for Puppy 4 series. It can be found as a .pet. gqview-2.0.4-i386.pet
Now superceded by other image viewing programs, it's still fast, and has a good array of features.